Electrical stimulation of predetermined locations within the cochlea of the human ear through an intra-cochlear electrode array is described, e.g., in U.S. Pat. No. 4,400,590. The electrode array shown in the '590 patent comprises a plurality of exposed electrode pairs spaced along and imbedded in a resilient curved base for implantation in accordance with a method of surgical implantation, e.g., as described in U.S. Pat. No. 3,751,615. The system described in the '590 patent receives audio signals, i.e., sound waves, at a signal processor (or speech processor) located outside the body of a hearing impaired patient. The speech processor converts the received audio signals into modulated RF data signals that are transmitted through the patient's skin and then by a cable connection to an implanted multi-channel intra-cochlear electrode array. The modulated RF signals are demodulated into analog signals and are applied to selected ones of the plurality of exposed electrode pairs in the intra-cochlear electrode so as to electrically stimulate predetermined locations of the auditory nerve within the cochlea.
U.S. Pat. No. 5,938,691, incorporated herein by reference, shows an improved multi-channel cochlear stimulation system employing an implanted cochlear stimulator (ICS) and an externally wearable speech processor (SP). The speech processor employs a headpiece that is placed adjacent to the ear of the patient, which receives audio signals and transmits the audio signals back to the speech processor. The speech processor receives and processes the audio signals and generates data indicative of the audio signals for transcutaneous transmission to the implantable cochlear stimulator. The implantable cochlear stimulator receives the transmission from the speech processor and applies stimulation signals to a plurality of cochlea stimulating channels, each having a pair of electrodes in an electrode array associated therewith. Each of the cochlea stimulating channels uses a capacitor to couple the electrodes of the electrode array.
A new, more sophisticated, class of cochlear implant, referred to as a bionic ear, is now available, providing patients with enhanced hearing performance. For example, Advanced Bionics® Corporation, of Sylmar, Calif., currently offers a cochlear implant which it refers to as the CII Bionic Ear® cochlear implant. Many features associated with the CII Bionic Ear® implant are described in U.S. Pat. No. 6,219,580, incorporated herein by reference. The added complexity of the CII Bionic Ear® cochlear implant includes higher numbers of channels, arbitrary simultaneous grouping, intra-phase gaps, binaural capabilities, and the like. The Bionic Ear implant contains advances in, e.g., internal memory banks, that enable it to send very detailed, high resolution sound signals to the auditory nerve. Such signals are delivered to the auditory nerve using a special electrode adapted to be inserted into the cochlea. A representative electrode usable with the CII Bionic Ear® is described in U.S. Pat. No. 6,129,753, also incorporated herein by reference.
Other improved features of cochlear implant systems are taught, e.g., in U.S. Pat. Nos. 5,626,629; 6,067,474; 6,157,861; 6,249,704; and 6,289,247, each of which is incorporated herein by reference.
The implantable cochlear stimulators described in at least the '629, '474, '861, '580, and '704 patents are able to selectively control the pulse width of stimulating pulses that are applied through the electrode array to the cochlea, and the frequency at which the stimulating pulses are applied.
When a cochlear prosthesis is first provided to a patient, it is necessary to initially “fit” or “adjust” the prosthesis. As used herein, it should be noted that the terms “fit”, “adjust”, “fitting”, “adjusting”, “program”, or “programming” relate to making electronic or software programming changes to the prosthesis, as opposed to making physical or hardware changes. Proper fitting allows the prosthesis to better perform its intended function of helping the patient to sense sound.
As the art of cochlear stimulation has advanced, the implanted portion of the cochlear stimulation system, and the externally wearable processor (or speech processor) have become increasingly complicated and sophisticated. In addition, much of the circuitry previously employed in the externally wearable processor has been moved to the implanted portion, thereby reducing the amount of information that must be transmitted from the external wearable processor to the implanted portion. The amount of control and discretion exercisable by an audiologist in selecting the modes and methods of operation of the cochlear stimulation system have increased dramatically and it is no longer possible to fully control and customize the operation of the cochlear stimulation system through the use of, for example, switches located on the speech processor. As a result, it has become necessary to utilize an implantable cochlear stimulator fitting system to establish the operating modes and methods of the cochlear stimulation system and then to download such programming into the speech processor. One such fitting system is described in the '629 patent. An improved fitting system is described in the '247 patent. The present invention is directed to simplified fitting systems that may be used with a variety of cochlear implants, such as those mentioned above.
The '247 patent describes representative stimulation strategies (a.k.a., speech processing strategies) that may be employed by a multichannel stimulation system. Such strategies define patterns of stimulation waveforms that are to be applied to the electrodes as controlled electrical currents. For instance, the speech processing strategy is used, inter alia, to condition the magnitude and polarity of the stimulation current applied to the implanted electrodes of the electrode array. If multiple electrode pairs exist, as is the case with a multichannel cochlear stimulator of the type used with the present invention, then the types of stimulation patterns applied to the multiple channels may be broadly classified as: (1) simultaneous stimulation patterns (substantially all electrodes receive current stimuli at the same time, thereby approximating an analog signal), or (2) sequential or non-simultaneous stimulation patterns (only one electrode receives a current pulse at one time). Simultaneous stimulation patterns may be “fully” simultaneous or partially simultaneous. A fully simultaneous stimulation pattern is one wherein stimulation currents, either analog or pulsatile, are applied to the electrodes of all of the available channels at the same time. A partially simultaneous stimulation pattern is one where stimulation currents, either analog or pulsatile, are applied to the electrodes of two or more channels, but not necessarily all of the channels, at the same time.
Typically, when the fitting systems described in the '629 or '247 patents or the like are employed for multichannel stimulation systems, it is necessary to use thresholds derived from the measurement of psychophysically-determined comfort levels. That is, for each channel, a minimum threshold level is measured, typically referred to as a “T” level, which represents the minimum stimulation current which, when applied to a given electrode associated with the channel, produces a sensed perception of sound at least 50% of the time. In a similar manner, an “M” level is determined for each channel, which represents a stimulation current which, when applied to the given electrode, produces a sensed perception of sound that is moderately loud, or comfortably loud, but not so loud that the perceived sound is uncomfortable. These “T” and “M” levels, a.k.a., iso-loudness contours, are then used by the fitting software in order to properly map sensed sound to stimulation current levels that can be perceived by the patient as sound.
Disadvantageously, current methods for determining the “T” and “M” iso-loudness contours (or other levels) associated with each channel of a multichannel stimulation system is an extremely laborious, time-intensive, and imprecise task. Such determinations require significant time commitments on the part of the clinician, as well as the patient. In addition, for some patients, especially those whose responses are difficult to obtain, e.g., very young patients, these levels may be quite subjective and dependent on the experience of the clinicians performing the fitting procedure.
Current cochlear implant fitting techniques, in addition to requiring considerable clinical and patient time, have not been amenable to auto-fitting or patient self-programming. Furthermore, when fitting patients using high rate stimulation, where the statistical variability of T and M iso-loudness contours increases substantially, a new technique is necessary for performing optimal patient fittings.